Microstructures of tungsten carbide (WC) particle reinforced high-speed steel composites fabricated by spray forming were observed by scanning electron microscope and transmission electron microscope. Experimental results show that the primary carbides of high-speed steel composites are MC and M6C. The high-speed steel composites reinforced by WC particles were investigated before and after heat treatment. It is shown that heat treatment may improve the bending strength and hardness of the composites in both as-sprayed state and as-treated state.